HARRISBURG — When you think of winter weather hazards, what comes to mind? Do you think of big snow storms that drop a significant amount of snow? Do you think of ice storms that cover trees, power lines, and roadways in a glaze of ice? Or maybe you think of flooding that can occur when a storm drops heavy rain on top of melting snow, overwhelming creeks, streams, and rivers with water?

Pennsylvania sees many forms of hazardous winter weather, including snow squalls. A snow squall is a brief but intense period of heavy snow (up to 2 inches in 30 minutes), strong winds (30+ mph), and whiteout conditions (visibility less than one-quarter of a mile). Snow squalls often occur on days with otherwise partly cloudy skies. Coming on so suddenly, snow squalls can catch drivers off guard and lead to major transportation impacts, including deadly multi-vehicle accidents.

One of the things that makes snow squalls so dangerous is their tendency to produce icy roadways. Since snow squalls usually occur on days with partly cloudy skies, road surface temperatures can start off well above the freezing point before snow squalls arrive. When the snowflakes start to fall, they initially melt on the warm road surface, making the road wet. However, as the snow becomes heavier and air temperatures fall, the road surface cools and water turns to ice. Ice can also form on road surfaces that start out below freezing, especially when moving traffic drives over fallen snow, packing it down and warming it just enough to become icy.

The National Weather Service (NWS) uses several tools to predict and detect snow squalls. First, forecasters analyze weather model simulations and apply the latest forecast methods to diagnose setups that are favorable for the development of snow squalls. When snow squalls are anticipated, the NWS gets the word out through forecast discussions, social media, and special weather statements. The NWS briefs partners, including the Pennsylvania Department of Transportation (PennDOT), Pennsylvania Emergency Management Agency (PEMA), and many others, including public safety and emergency management officials. Broadcast meteorologists also do a great job in getting the forecast out to the public.

If you do get caught driving in a snow squall, avoid slamming on your brakes, turn on your headlights and hazard lights, stay in your lane, and increase your following distance.